Crop rotation complexity regulates the decomposition of high and low quality residues

While many ecosystem processes depend on biodiversity, the relationships between agricultural plant diversity and soil carbon (C) and nitrogen (N) dynamics remains controversial. Our objective was to examine how temporal plant diversity (i.e. crop rotation) influences residue decomposition, a key ecosystem function that regulates nutrient cycling, greenhouse gas emissions, and soil organic matter formation. We incubated soils from five long-term crop rotations, located at W.K. Kellogg Biological Station LTER in southwestern Michigan, USA, with and without four chemically diverse crop residues. Increasing crop biodiversity increased soil potentially mineralizable C by 125%, increased hydrolytic enzyme activity by 46%, but decreased oxidative enzyme activity by 20% in soils before residue was added. After residue additions, soils from more diverse cropping systems decomposed all residues more rapidly (0.2–8.3% greater mass loss) compared to monoculture corn. The fast-cycling, ‘Active C’ pool and microbial biomass N increased with higher cropping diversity, but the differences among rotations in Active C pools was higher for the most recalcitrant residues. Further, the ratio of the cellulose degrading enzyme (β-glucosidase) to the lignin degrading enzyme (phenol oxidase) was highest in the two most diverse crop rotations regardless of residue additions, providing additional evidence of enhanced microbial activity and substrate acquisition in more diverse rotations. Our study shows that crop diversity over time influences the processing of newly-added residues, microbial dynamics, and nutrient cycling. Diversifying crop rotations has the potential to enhance soil ecosystem functions and is critical to maintaining soil services in agricultural systems.     

Stand restoration burning in oak–pine forests in the southern Appalachians: effects on aboveground biomass and carbon and nitrogen cycling

Understory prescribed burning is being suggested as a viable management tool for restoring degraded oak–pine forest communities in the southern Appalachians yet information is lacking on how this will affect ecosystem processes. Our objectives in this study were to evaluate the watershed scale effects of understory burning on total aboveground biomass, and the carbon and nitrogen pools in coarse woody debris (CWD), forest floor and soils. We also evaluated the effects of burning on three key biogeochemical fluxes; litterfall, soil CO₂ flux and soil net nitrogen mineralization. We found burning significantly reduced understory biomass as well as the carbon and nitrogen pools in CWD, small wood and litter. There was no significant loss of carbon and nitrogen from the fermentation, humus and soil layer probably as the result of low fire intensity. Burning resulted in a total net loss of 55 kg ha⁻¹ nitrogen from the wood and litter layers, which should be easily replaced by future atmospheric deposition. We found a small reduction in soil CO₂ flux immediately following the burn but litterfall and net nitrogen mineralization were not significantly different from controls throughout the growing season following the burn. Overall, the effects of burning on the ecosystem processes we measured were small, suggesting that prescribed burning may be an effective management tool for restoring oak–pine ecosystems in the southern Appalachians.     

不同森林类型枯落物持水特性研究

通过对贵州天然林资源保护工程区128个样地调查,将采集的枯落物进行持水特性试验分析,得出了不同森林类型的枯落物储量和持水特性以及不同主要树种组成的林分枯落物储量和持水特性的差异。     

梵净山不同植被类型枯落物持水特性研究

本文对贵州梵净山自然保护区内6种不同植被类型枯落物的储量、枯落物吸水速率和持水能力进行了分析,发现不同植被类型在枯落物储量、持水量、持水率和吸持水速率上有差异:马尾松栲树混交林和亮叶水青冈八角阔叶林的枯落物储量大于其它几种森林类型,丝栗栲纯林的枯落物储量最小;马尾松栲树混交林和栲树纯林的持水率明显低于其它几种植被类型的持水率,在吸水速率上也慢于其它几种植被类型;润楠属植物为主的枯落物持水率明显高于其它几种常绿落叶阔叶林,吸水速率也明显快于其它几种常绿落叶阔叶林。     

天山森林凋落物和枯枝落时层的研究

通过１９９２－１９９５年的定位试验，对天山森林凋落物和枯枝落叶的主要性质进行了研究。结果表明，天山森林生态系统中养分运转具有独特性：（１）森林年凋落量较低，为２．１ｔ／ｈｍ＾２凋落物的季节动态变化呈单蜂型；（２）以凋落物形式的养分年归还量为Ｃａ〉Ｎ〉Ｋ〉Ｐ。在凋落之前，大部分Ｎ、Ｐ、Ｋ被转移，Ｋ的转移量最大，而Ｃａ则相对富集，归还量最小；（３）枯枝落叶层中养分贮量和蓄水量高，但有机物质分解率较低；     

Best among unequals? Effect of size grading and different social environments on the growth performance of juvenile Atlantic halibut

In order to study the effect of rearing juvenile halibut in different social environments, individually tagged juvenile halibut were size-graded into two size classes (Large, L, and Small, S) with ungraded fish as control. After ca 6 weeks, the two size-graded groups were again graded into two size classes creating four experimental groups: Large of the Large (LL), Small of the Large (SL), Large of the Small (LS), and Small of the Small (SS). Grading (overall mean of the four grading groups) improved growth rate by 10% compared with ungraded controls, but the effect was also significantly affected by social environments, because in the latter half of the experiment overall growth was improved by 11 and 12% in the two groups with larger size variation (i.e. SL and LS, respectively) compared with the two other groups (i.e. LL and SS). Significant size rank correlations were maintained during the experiment, these were higher in the ungraded (Control) group and the SS and LL groups than in the SL and LS groups. Further, the degree of mean rank position changes varied between the experimental groups and was higher in the SL (20.7) and LS (25.6) groups than in the Control (10.5), LL (15.1), and SS (15.4) groups. This could possibly indicate a stronger social hierarchy in the last three groups. Growth rate differences may be the product of different degrees of interactions among individuals, and based on the higher overall growth rates in the groups with larger size variation (i.e. SL, LS) it is concluded that juvenile halibut should not be too intensively size graded. Imsland and Jenssen have contributed equally.     

不同类群大白猪窝产仔数的遗传分析

对双肌臀大白猪和普通大白猪组成的 561窝产仔数的资料进行了遗传分析。结果表明 :公猪和胎次均对母猪产仔数 (总产仔数和活产仔数 )具有极显著影响 (P <0 .0 0 1 ) ,季节和类群均对母猪产仔数 (总产仔数和活产仔数 )具有显著影响 (P <0 .0 5)。大白猪产仔数的平均值随胎次增长而增加。夏季分娩的大白猪具有最高的产仔数 ,依次为春季和冬季 ,秋季最低。大白猪总产仔数和活产仔数的遗传力分别为0 .0 9和 0 .1 0 ,属低遗传力 ,直接选择窝产仔数几乎没有效果 ;它们之间的遗传相关为 0 .80 ,表型相关为0 .85,环境相关为 0 .90 ,它们之间的协遗传力为 0 .0 8。这些参数表明总产仔数和活产仔数是两个不同的性状 ,在生产实践中单独记录它们是有理由的、必要的。     

辊压处理大青杨板材的形体变化规律

常温下，以压缩率10％、20％、30％、40％和50％5个条件对饱水状态的大青杨(P．ussuriensis Kom)板材分别进行无约束径向和弦向辊压处理；研究辊压处理前后在全干、气干(含水率12％)和饱水3种测试状态下，试材在厚度、宽度和体积3个方面的尺寸形体变异及单位尺寸和体积变化的百分率。相对于压缩前，总体变化规律为：辊压所致瞬时变形在其后绝大部分可恢复，辊压后试材厚度方向尺寸变小(-0．154％～-4．500％)、宽度方向尺寸略变大(0～3．740％)、体积略为降低(-0．329％～-3．019％)。     

模拟增温增水对克氏针茅草原主要物种及群落凋落物分解的影响

应用开顶式生长室（OTC, Open Top Chamber）模拟增温,以自然状态为对照,设增温(W)、增水（P）和增温+增水（WP）3个处理,对克氏针茅草原主要物种克氏针茅(Stipa krylovii)、糙隐子草(Cleistogenes squarrosa)、冷蒿（Artemisia frigida）以及群落凋落物的分解速率进行试验研究。结果表明：(1)经过1a的分解,W处理下各物种凋落物质量残余率高于CK,即增温减缓了凋落物的分解;WP处理对凋落物质量残余率的影响与W处理一致,但其增温的影响程度更大;P处理下凋落物残余率与CK无显著差异。(2) 增温对不同种类凋落物分解进程无显著影响;而增水明显加快了糙隐子草的分解进程;增温+增水对冷蒿的分解进程影响较大,但最终各物种凋落物残余率差异不显著。(3)对残余率变化动态的方差分析表明,增温增水对凋落物分解的影响主要与凋落物种类以及分解时间的长短有关。(4)采用Olso负指数模型模拟凋落物质量损失变化过程,增温条件下,除冷蒿外,其它各种凋落物的k值（表征分解速率）均低于CK;增水条件下,克氏针茅和糙隐子草的k值低于CK,而冷蒿和群落凋落物的k值高于CK;增温+增水条件下,不同种类凋落物k值的变化与W处理一致,但整体上WP处理下凋落物的k值高于W处理。根据研究结果可以推断出,未来气候变化下内蒙古克氏针茅草原凋落物的分解将趋于减缓。     

不同林龄澳洲坚果园凋落物与土壤养分的关系

对桂西南地区3个龄级(6、8、10 a)的澳洲坚果(Macadamia ternifolia)经济林的凋落物组成和土壤养分的变化进行研究。结果表明:凋落物量的大小为落叶(3 202.48 kg/hm~2)落果(830.24 kg/hm~2)枯枝(427.13 kg/hm~2)落花(246.49 kg/hm~2),总量为4 706.34 kg/hm~2,凋落物叶的含量占68.05%;凋落物每年养分归还量表现为落叶(1 416.46 kg/hm~2)落果(367.22 kg/hm~2)枯枝(188.92 kg/hm~2)落花(109.02 kg/hm~2),养分含量表现为碳(1 953.55 kg/hm~2)氮(72.81 kg/hm~2)钾(50.17 kg/hm~2)磷(5.08 kg/hm~2),碳占主体,达93.84%。随着林龄的增长,土壤养分含量平均表现出全碳(58.03 g/kg)全氮(6.88 g/kg)全钾(5.77 g/kg)全磷(0.24 g/kg),不同的土壤养分随凋落物养分回归具有差异性,土壤碳、氮都与凋落物氮呈负相关,而与凋落物磷和钾呈正相关;土壤磷与凋落物氮呈负相关,而与凋落物碳和钾呈正相关;土壤钾与凋落物氮和钾呈负相关,而与凋落物碳和磷呈正相关。因而凋落物是澳洲坚果园土壤肥力培育需要考虑的重要因素之一。